Traumatic Meniscus Tears

A meniscus that is forcefully pinched between the femur and tibia during a knee sprain injury may tear, even if it is strong, youthful and undegenerated. Such tears are called "traumatic" because they occur suddenly and because the meniscus would not have failed at that time were it not for the highly stressful knee sprain. With few exceptions, simultaneous weight-bearing and joint rotation (as are typically seen in a wrenching, sprain-type injury) are required to tear a meniscus, as without the former, no impingement ("pinching") forces are experienced by the meniscus.

FIGURE 2 - Schematic diagram demonstrating the vascular (blood vessel) supply of the meniscus, which enters through the meniscus' attachment to the knee's capsular ligament.

Only the outer (more peripheral) 30-40% of a meniscus actually has a capillary blood supply (see FIGURE 2) and thereby a significant potential for healing when injured. Sometimes a traumatic tear will involve this peripheral, vascular (or so-called "red") zone of the meniscus, whereas at other times it will also (or only) involve the avascular (non-bleeding or so-called "white") zone, which is in the inner 2/3 of the meniscus (see FIGURE 3). Relatively vertical (straight split), traumatic tears in the peripheral 1/3 of the meniscus have good healing potential, thus are almost always surgically repairable. Tears in the inner, avascular "white" zone of the meniscus do not bleed and are rarely good candidates for surgical repair (at least with current technology), as their healing potential is much more limited. Even if such tears seem to heal initially, following a repair procedure, they have a fairly high chance of breaking down again, thus requiring another surgical procedure (meniscectomy) to excise them in the future.

FIGURE 3 - Diagrammatic representation of a torn meniscus (a so-called peripheral, longitudinal tear), seen in cross-section. The "tear" is the curved, split-defect that you see in between the peripheral red zone and the inner white zone. The peripheral red zone in the outer 1/3 of the meniscus is the only portion of the meniscus that has a capillary blood supply (see Figure 2). Traumatic meniscal tears within or at the edge of this vascular zone will bleed and thereby have the potential to heal if treated properly, so they should be repaired whenever possible. Tears in the inner, thinner, avascular (white) zone do not bleed and have a far lesser potential for stable healing. They are, therefore, significantly less amenable to repair. This is true even if the meniscal tissue was healthy and non-degenerated prior to failing.